Determination Of The Absolute Structure Factor For The Forbidden (222) Reflection In Silicon Using 0.12-γ Rays

A room-temperature determination of the absolute structure factor for the forbidden (222) reflection in silicon has been conducted at the University of Missouri Research Reactor with 103-keV gamma rays. The measured structure factor of F(222)=1.456 is in excellent agreement with five of the earlier intensity measurements and is significantly different from any value determined using Pendellösung techniques. An increase in accuracy over previous intensity measurements by a factor of between 2 and 10 has been achieved and is made possible through the use of monoenergetic, short-wavelength gamma rays, which allow absolute measurements to be made in Laue geometry on relatively thick crystals (∼1 mm) without encountering extinction problems. © 1982 The American Physical Society

Coupled Electrical and Magnetic Properties in (La,Sr)FeO\u3csub\u3e3-δ\u3c/sub\u3e

This article is aimed at studying the temperature dependence oxygen nonstoichiometry, magnetic moments, Fe3+ fraction, Néel temperature and conductivity of (La,Sr)FeO3-δ. It is found that the magnetic properties in La0.60 Sr0.40 Fe3-δ is determined by Fe3+ and its concentration, and the conductance is resulted from Fe4+ ions, which act as electron holes. Both of magnetic and electrical properties were directly governed by oxygen nonstoichiometry (δ). when δ=0.2, the compound has maximum Fe3+, the saturation magnetic moments and Néel temperature are 3.8 µB and 410 °C, both at the highest level, whereas the total carrier concentration is at the minimum

Crystal Perfection Of HgI2 Studied By Neutron And Gamma-ray Diffraction

The crystalline perfection of wire sawn pieces of vapor grown single crystals of mercuric iodide was compared with the perfection of (00l) cleaved sections of the same crystal from which nuclear radiation detectors have been fabricated. The crystalline perfection was studied using neutron and gamma-ray diffraction rocking curves. Most of the gamma-ray data were obtained using a high intensity source of 153Sm gamma rays with a wavelength of λ = 0.12 Å. Some of the data were obtained using highly penetrating 198Au gamma rays with a shorter wavelength of λ = 0.03 Å. The neutrons had a wavelength of λ = 1.07 Å. It was found that, in terms of the mosaic spread of the crystals, the cleaved detector plates have a much lower crystalline perfection than the thicker uncleaved detector plates. At the same time, the results show that for detectors cut from the same crystal, the one with the lower spectral resolution for radiation detection will also have a lower perfection and larger width of the gamma-ray rocking curve. These results suggest consideration should be given to alternative fabrication procedures for HgI2 nuclear radiation detectors

Studies of V, Nb, Cr, and Zr Substituted 2:17 Compounds and their Carbides using Neutron Diffraction

Samples of Nd2Fe17-xTxCy with T=V, Nb, Cr, and Zr were prepared by melting of the constituent elements including C and studied by neutron diffraction. Comparing with their uncarbided counterparts, we found that the substituents transfer, more or less, from the 6c site to the 18f and 18h sites with the introduction of C atoms. This behavior appears to relate to the electronegativities between the C atoms and the early transition series elements because the 18f and 18h sites are near neighbors of the interstitial C site. However, the C effects in the V. Nb. Cr, and Zr samples are not as strong as those in Ti samples. SQUID measurements show that the Curie temperatures of these samples depend on both the interstitial C atoms and the substituents

The University Of Missouri Gamma-ray Scattering Facility

The field of gamma-ray scattering is new and only a few of the possible applications of the technique have been pursued. At the University of Missouri Research Reactor (MURR) we are presently completing two instruments to perform studies not previously attempted. The first instrument is a full-circle diffractometer with additional differential ω-motion and linear drive system for the detector which will be used for accurate crystallographic structure measurements at either 0.125 Å (153Sm) or 0.03 Å (198Au). The reduced absorption and extinction at these wavelengths should permit more accurate structure factor determination than has been possible with either X-rays or neutrons. A unique source irradiation system and shield cask have been designed to permit the utilization of relatively large, extremely intense sources. The cask is self-centering at the instrument and has a built in rotation of the source container to maximize the intensity. A large exit aperture is provided in the vertical direction (∼3″) to give extra intensity when tight collimation is not required in that direction. The second instrument will be using the 103 keV photons from 153Sm as a Mössbauer source and will detect inelastically scattered photons with a centrifugally driven absorber. Because of the high specific activities attainable in the flux trap at MURR (∼6000 Ci/g for enriched 152Sm) these experiments should be possible where such studies with traditional sources, e.g., 57Fe, have not succeeded. © 1979

Fabrication Of HgI2 Nuclear Radiation Detectors By Machine Cleaving

A new device has been designed to facilitate the cleaving of thin sections from bulk crystals of mercuric iodide. Crystallographic perfection of the machine-cleaved sections was established by gamma-ray diffraction rocking curves and was found to be higher than the perfection of hand-cleaved sections or of as-grown thin platelets, approaching the perfection of string-sawn section of HgI2. A correlation was found between the perfection and thickness of the machine-cleaved sections, i.e., the thicker the section the more perfect it is. Reproducibility of the fabrication was significantly improved by using machine cleaving in the fabrication process. © 1983

A Search for Magnetic Resonance of Ruthenium in Octahedral Coordination with Oxygen

We have searched, without success, for microwave-frequency magnetic resonance of Ru4+ and Ru5+ ions in a number of materials for which the Ru are in octahedral coordination with six oxygen. A number of ruthenates including RuO2, SrRuO3, Sr3Ru2O7, Ba3Ru2NiO9, Ba2GdRuO6, Sr2YRuO6, and Ba2YRuO6, which include paramagnetic, antiferromagnetic, and ferromagnetic spin configurations, have been examined. We present analysis which shows that the last material provides an optimized opportunity to detect antiferromagnetic Ru resonance for temperatures less than TN=39 K; none is detected for frequencies as high as 35 GHz in magnetic fields up to μoH=2 T. This result indicates that the antiferromagnetic magnon energy gap exceeds the energy associated with the signal frequency. SrRuO3 is a known ferromagnetic contaminant phase in the rutheno-cuprates. We report neutron diffraction measurements on SrRuO3, finding it to have an appreciable local moment at low temperatures, 1.25(0.1)μB; this moment vanishes near 165 K. We show that it also fails to exhibit ferromagnetic resonance, at least in the range 10-35 GHz. As a result of the diffraction and resonance studies, it is concluded that the reports of ferromagnetic resonance in superconducting rutheno-cuprates are actually due to antiferromagnetically ordered Cu in these materials, and the presence of even a few percent of SrRuO3 as a potential contaminant is of little importance

Mixed Rare-earth Effects in (Sm/Gd)₂(Fe/Si)₁₇ Intermetallics

The affects of mixing samarium and gadolinium on the crystallographic and magnetic properties of SmyGd2-yFe17-xSix (x = 0, 0.33, 0.67, 1, 2, 3 and y = 0.33, 0.67, 1, 1.33, 1.67) intermetallics have been investigated using x-ray diffraction techniques and SQUID and Vibrating Sample Magnetometer measurements. The SmyGd2-yFe17-xSix samples, except for the sample with x = 3 and y = 1, crystallized in the rhombohedral Th2Zn17-structure with little or no impurities. For a given silicon content (fixed x), the unit cell volume and saturation magnetization increases at the approximate average rates of 4 Å3 and 24 emu/g per substituted samarium atom, respectively. The Curie temperature (Tc) for a given silicon content, on the other hand, decreases with increasing samarium content at an average rate of 30-40 °C per substitution. The affect of substituting silicon for iron on Tc is more marked, with Tc increasing at a rate of almost 70 °C per silicon substitution at low silicon concentrations. For a given samarium content (fixed y), the unit cell volume and saturation magnetization decreases at approximate rates of 5 Å3 and 9 emu/g per substituted silicon atom, respectively. X-ray diffraction studies of magnetically aligned powders indicate that the easy direction of magnetization is in the basal plane of the rhombohedral unit cell. All of the samples were found to have very little magnetic anisotropy with no apparent dependence of the anisotropy on the samarium or silicon content. The 340 °C Tc measured for the SmGdFe14Si3 sample is unusually high for these intermetallics and its XRD pattern is indicative of a phase other than the rhombohedral Th2Zn17-type

Electrical, Thermoelectric, and Structural Properties of La(MₓFe₁₋ₓ)O₃ (M=Mn, Ni, Cu)

Electrical, thermoelectric, and structural properties were studied in transition metal ion-substituted LaFe O3: La (Mnx Fe1-x) O3, La (Nix Fe1-x) O3, and La (Cux Fe1-x) O3. Structural analysis showed that a continuous series of solid solutions with no intermediate phases are forming over a wide range (